1. Field of the Invention
The present invention relates to an image sensor apparatus which is installed in an image input apparatus such as a facsimile and a hand-held scanner.
2. Description of Related Art
A fully contact type image sensor apparatus is conventionally known which is installed in a small image input apparatus such as a facsimile and a hand-held scanner. FIG. 1 is a perspective view illustrating the first conventional example of a fully contact type image sensor apparatus 50. Also, FIG. 2 is a cross sectional view illustrating the first conventional example of the image sensor apparatus cut along the line X--X in FIG. 1. Referring to FIGS. 1 and 2, the first conventional example of image sensor apparatus 50 is composed of a linear light source 60, a linear image sensor section 70, and an optical fiber binding section 80.
The linear light source 60 is composed of a printed circuit board 61, a reflection frame 62, and a cylindrical rod-shaped lens 63. The printed circuit board 61 is provided for a plurality of light emitting elements 64 to be arranged in a linear manner on the lower surface of the printed circuit board 61, Also, a reference numeral 65 denotes a wiring for connecting the light emitting element 64 to the printed circuit board 61.
The linear image sensor section 70 is composed of a transparent substrate 71 and a train of pixels 72. The train of pixels 72 includes photoelectric converting elements of thin film semiconductor elements which are formed of amorphous silicon. The train of pixels 72 is provided in the lower portion of the transparent substrate 71.
The optical fiber binding section 80 is composed of an optical fiber section 81 and a support body 82. In the optical fiber section 81, a plurality of optical fibers 81A are bound to turn to upper and lower directions in FIG. 2. The support body 82 supports the optical fiber section 81. The one end of the bunch of the plurality of optical fibers 81A is fit in a facing state to the pixel train 72 and the other end faces a manuscript P.
Next, the operation of the above-mentioned first conventional example of an image sensor apparatus will be described below.
First, light is emitted in all directions from the light emitting surface of each of the light emitting elements 64 and converged in a linear manner along the longitudinal direction of the cylindrical lens 63. After passing the transparent substrate 71 and the gaps between the pixels of the train 72, the converged light is incident into the optical fiber section 81. The light which has passed through the plurality of optical fibers 81A irradiates the manuscript P. The light reflected from the manuscript P passes through the same optical fibers 81A and is detected by the pixel train 72. In this manner, black and white information of the manuscript P can be obtained.
In this case, in order to improve the quality of the image obtained by the image sensor apparatus, it is generally desirable that an illumination distribution of light on the manuscript P is uniform. In this conventional example, however, the illumination distribution varies in accordance with a numerical aperture (NA) of the optical fibers 81A.
FIG. 3 is a diagram illustrating an illumination distribution. In FIG. 3, each of the dashed lines corresponds to a region where each of the light emitting elements 64 is provided. As seen from FIG. 3, if the numerical aperture of each of the optical fibers 81A is small, there is a remarkable difference in the illumination distribution between the regions downward corresponding to a region between every adjacent two of the light emitting elements 64 and the region downward corresponding to each of the light emitting elements 64. According to the illumination distribution shown in FIG. 3, the illumination on the manuscript P decreases most in the regions of the manuscript P which correspond to the regions between every adjacent two of the light emitting elements 64. This is because the light emitted by the light emitting elements 64 reaches the optical fibers 81A with an inclined angle larger than a critical angle determined by the numerical aperture NA of each optical fiber, so that the light can not be transferred inside the optical fibers 81A.
If the optical fiber binding section 80 composed of a plurality of optical fibers 81A having a large numerical aperture NA is used, a good uniformity in the illumination distribution can be achieved. However, if there is a gap between the manuscript P and the optical fiber binding section 80, the reflected light is detected from a region wider than a predetermined area of the manuscript P. Therefore, the image quality (resolution) tends to degrade.
In this way, in the first conventional example of the image sensor apparatus 50, there is a problem of illumination uniformity. The uniformity of the illumination distribution on the manuscript P is degraded when the optical fibers 81A having a small numerical aperture NA is used. The resolution is easily degraded by the presence of a gap between the manuscript P and the optical fiber binding section 80 when the optical fibers 81A having a large numerical aperture NA are used.
Next, the second conventional example of an image sensor apparatus is disclosed in Japanese Laid Open Patent Disclosure (JP-A-Heisei 5-227367). FIG. 4 is a vertical cross sectional view of the second conventional example of an image sensor apparatus and FIG. 5 is a horizontal cross sectional view for some of its components.
As shown in FIG. 4, the second conventional example of the image sensor apparatus is composed of a linear light source 92, an optical section 91, an array of gradient index optical fibers 95 and a linear image sensor section 96 mounted on a printed circuit board 97. The linear light source 92 is composed a plurality of light emitting diodes 93 which are arranged in a linear manner and irradiate a manuscript P through the optical section 91. The array of gradient index optical fibers 95 focuses the light reflected from the manuscript P on the linear image sensor section 96. The linear image sensor section 96 reads an image of the manuscript P by detecting the reflected light focused by the array of gradient index optical fibers 95.
Here, the optical section 91 is provided with convex portions 99, each of which has the length equal to the separation between the two adjacent light emitting diodes as shown in FIG. 5. This optical section 91 improves the uniformity of the manuscript illumination by changing the direction of light via refraction. It is necessary for the convex portions 99 to have the thickness in correspondence to the arrangement pitch.
However, the arrangement pitch of the light emitting diodes is determined by taking the illumination uniformity and a manufacturing cost into account and is usually equal to or larger than 3 mm. For this reason, if the above-mentioned second conventional example is applied for the fully contact type image sensor apparatus as shown in FIG. 1, the apparatus would have a large-sized structure. As a result, the advantage of the fully contact type image sensor apparatus is lost.